1,720,987 research outputs found
Surface Photovoltage studies of surface and defect states in semiconductors
No full textThe Surface photovoltage spectroscopy (SPS) is a valuable and flexible method for the non-contact and
non-destructive investigation of electronic states in semiconductors [1,2]. In this contribution, a throughout
description and discussion of the SPS method will be presented. The basic physical principles, the details of
the experimental set-up and the relevant results, the capability of the method to extract material
properties like optical band gap and defect related states will be discussed. The method presents several
advantages, as it allows for the identification of conduction vs. valence band nature of the defect-related
transitions and the defect level positions within the band gap. Moreover it allows for the detection of
relatively low densities of surface defects as well as their cross sections.
Some examples of the application of the method to different materials and structures are discussed,
ranging from bulk semiconductors, to low-dimensional systems, to nano- structures.
In more detail, SPS has been used to determine the energy gap of bulk crystalline CdTe and Cd1-xZnxTe, and
its variation with Zn concentration, to determine surface recombination effects and below-band gap defect
states.
SPV spectroscopy has also allowed for optical characterization of buried layers in III-N based
heterostructures, where the effect that the 2 dimensional electron gas forming in InAlGaN/GaN has on the
energy gap value has been demonstrated. Impurity related levels, gap values and bowing parameters have
been obtained in InxGa1-xN as a function of In content.
The potentialities of the method have further been shown on Si based nanostructures, in this case the
method helped obtaining evidence of quantum confinement in Si nanocrystals and doping-induced phase
changes in Si nanowires. Finally, the application of the method to nanoporous Ge has contributed to the
identification of phase transitions induced by thermal treatment, quantum confinement effects and
enhanced light trapping effects due to Au nanoparticles embedded in the np-Ge matrix.
In conclusion, the here reported examples evidence the potential, the flexibility and the ease of application
of the SPV method, that can be used to investigate a wide range of different systems allowing to achieve
relevant physical information on material properties that can hardly be otherwise obtained.
References
1. Kronik L. Shapira Y. 2001. Surface photovoltage spectroscopy of semiconductor structures: at the
crossroads of physics, chemistry and electrical engineering. Surf. Interface Anal.; 31, 954–965.
2. D Cavalcoli, B Fraboni, A. Cavallini; Surface and Defect States in Semiconductors Investigated by
Surface Photovoltage, Chapt 7, Semiconductors and Semimetals, Elsevier, 91, 251-278, 2015
Surface and Defect States in Semiconductors Investigated by Surface PhotovoltageDefects in Semiconductors
No full textThe aim of this chapter is a throughout description and discussion of surface photovoltage spectroscopy. The basic physical principles, experimental details, and relevant results of the method are described, and the capability of the method to extract material properties like optical band gap and defect-related states is discussed. The method presents several advantages, as it allows for the identification of conduction versus valence band nature of the defect-related transitions and the defect level positions within the band gap. Moreover, it allows for the detection of relatively low densities of surface defects as well as their cross-sections. The application of the method to different materials and structures is discussed, ranging from bulk semiconductors to low-dimensional systems, to nanostructures
Optical and electrical characterization of ternary and quaternary gallium nitride based alloys
No full textProgress in epitaxial growth techniques in the last 20 years has led to the availability of high quality ternary (InGaN) and quaternary (AlInGaN) alloys for optical devices [1], high efficient solar cells, high electron mobility transistors, microwave power applications [2] and, recently, photo-electrochemical (PEC) devices for water splitting cells [3].
Their most interesting feature is the bandgap tunable with composition, covering the whole visible spectrum. Despite extensive research on In-based alloy systems, the dependence of the bandgap, polarization properties, role of dislocations and strain relaxation mechanism on the In-content is still debated, and the effect of crystal defects on optical and electrical properties of heterostructures based on InxGa1-xN and AlxInyGa1-x-yN alloys is not yet clear.
This contribution presents the results of electrical and optical characterization of InxGa1-xN/GaN and AlxInyGa1-x-yN/GaN structures by Surface Photovoltage (SPV) Spectroscopy and deep level transient spectroscopy (DLTS) in correlation with Transmission electron microscopy analysis (TEM) and light-assisted Kelvin probe force microscopy (KPFM). The influence of In content and Si-doping concentration on the misfit dislocations and electronic transitions in InxGa1-xN layers has been investigated has been discussed. Furthermore, the two-dimensional electron gas at the AlxInyGa1-x-yN/GaN heterointerfacehas been characterized by SPV and the main recombination centers in quaternary AlxInyGa1-x-yN/GaN alloys have been determined in terms of its activation enthalpy and capture cross-section. Furthermore, light-assisted KPFM reveals direct visualization of sites associated with recombination centers/traps, which includes threading dislocations, misfit dislocations and coalescence boundaries.
The present analysis has allowed us to clarify the role of In content and misfit dislocations on alloy disorder and to characterize the defects acting as strong recombination center in ternary and quaternary GaN based alloys.
[1] S. Nakamura et al., Proc. IEEE 101, 2211 (2013).
[2] N. M. Johnson et al., Phys Today 53, 31 (2000).
[3] J. Jia et al., Nat. Commun. 7, 13237 (2016)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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